chore: add @tailwindcss/postcss and PostCSS setup for Tailwind v4

tests/e2e/example.spec.ts

@@ -0,0 +1,10 @@
+import { test, expect } from '@playwright/test'
+
+test('happy path: home loads and increments', async ({ page }) => {
+  await page.goto('/')
+  await expect(page.getByRole('heading', { name: 'Welcome' })).toBeVisible()
+  await page.getByRole('button', { name: /Increment/ }).click()
+  await expect(page.getByText(/Count: 1/)).toBeVisible()
+})
+
+

tests/example.spec.ts

@@ -0,0 +1,9 @@
+import { describe, it, expect } from 'vitest'
+
+describe('math', () => {
+  it('adds', () => {
+    expect(1 + 1).toBe(2)
+  })
+})
+
+